The invention relates to a device for regulating the idling speed of an internal combustion engine.
A device for regulating the idling speed of an internal combustion engine by varying the feed comprises an electromechanical setting member which has electromagnetic means which are developed as solenoid and have at least one coil, ferromagnetic parts conducting magnetic flux, at least one core which can be influenced by the flux and a magnetic flux-conducting element connected to the core for adjusting a valve element against a return force, as well as means for maintaining the valve element in a position of medium rate of air flow upon an interruption in the feeding of setting current to the coil.
Devices are used to regulate the idling speed in order, in particular in automotive vehicles, to set the lowest possible speed of rotation which results in favorable consumption and emission values. With constant feed of the internal combustion engine, variations in idling speed may occur, in particular, due to different loads caused by auxiliary units. In addition to this, at low idling speed the operating condition of an internal combustion engine is close to the unstable speed range within which the engine may stall upon further additional load. For this reason, the rate of flow of the air or the feed upon idling is not permanently set but is regulated in accordance with the variations in the idling speed. For this purpose, a solenoid is acted on by a setting current which is formed, inter alia, as a function of the actual speed of rotation and which effects such a displacement of the valve element connected to the solenoid that the actual speed of rotation reaches a predetermined desired speed substantially independently of any disturbing variables.
Normally, known devices for regulating the idling speed are developed in detail in such a manner that when the solenoid is without current the valve element is held either in the fully open or fully closed position by the return spring. Only when the solenoid is acted on by the setting current does the valve element move against the force of the return spring into a middle position between said two end positions until equilibrium prevails between the magnetic force and the force of the return spring.
In the case of a failure of the device which produces the setting current or of a disturbance in the solenoid, the internal combustion engine will accordingly be operated either with the greatest possible rate of flow of air in the idling range, which normally results in an undesirably high idling speed, or else with a minimum rate of flow of air with the danger of stalling.
In order that even in the event of the failure of the solenoid or of the current actuating it there is automatically set a medium idling rate of flow of air which makes it possible to expect an idling operation which is satisfactory for most conditions of load of the internal combustion engine, a device of the aforementioned type has been proposed. It is characterized by the features that a ferromagnetic actuating element is arranged within the region of influence of the solenoid, the said element being displaceable by at least one auxiliary spring with respect to the valve element up to a stop which is in fixed relationship to the valve element, and that the auxiliary spring is so dimensioned relative to the return spring that when the solenoid is without current, the valve element is maintained in the position of medium rate of flow of air by the action in opposite directions of the auxiliary spring and the return spring.
The automatic setting of a medium rate of flow of air when the solenoid is without current is obtained, in accordance with a previous system, by the action of the auxiliary spring, via the actuating element, on the valve element in opposition to the force of the return spring. When the solenoid is without current, the actuating element is, namely, held against the stop by the auxiliary spring and thereby positions the valve element in a medium position while, without the auxiliary spring, the valve element would be held in an end position by the action of the return spring. In this medium position of the valve element an equilibrium of forces has been established by the deformations of the return spring and auxiliary spring which correspond to this position. On the other hand, if the solenoid is acted on by a setting current when the control is properly operating, it attracts the ferromagnetic actuating element against the force of the auxiliary spring so that the actuating element is detached from the stop. As a result, the valve element is adjusted, as customary, independently of the actuating element and the auxiliary spring, solely in accordance with the equilibrium of forces between the solenoid and the return spring. The function of the actuating element presupposes such a development of the solenoid that the magnetic fluxes can pass from the solenoid into the region of the ferromagnetic actuating element so as to produce the desired action of force on the latter. The solenoid, therefore, must not be completely magnetically closed in the region of the actuating element. This device results in considerable additional expense in the region of the solenoid. In addition, this device, in the same way as similar devices which do not provide for additional measures for setting a medium rate of idling-air flow, tends to operate with a non-linear course of the force/stroke curve. This is due in particular to changes in the air gap as a function of the solenoid. It has heretofore been attempted to straighten the curve by having parts of the magnet which conduct magnetic flux excited up to magnetic saturation in individual regions. Due to the relatively poor magnetic conductivity within the saturation region this, however, necessarily resulted in a reduction in the force which could be used for the displacement of the valve element.
It is an object of the invention to develop a device of the aforementioned type in such a manner that the device assures a medium rate of flow of air upon idling operation when the setting current or solenoid has failed, by means having few mechanical parts and that it makes possible, in disturbance-free operation, a substantially linear course of the force/stroke curve as well as relatively large setting forces.